1. Field of the Invention
The present invention relates to optically transparent heat and impact resistant polyurethane.
2. Background of the Invention
Currently, the standard material to which all optically transparent plastic materials are compared to for impact resistance is polycarbonate. These materials can be characterized by the temperature and pressure at which the material undergoes distortion. The heat distortion temperature of 9034 series clear polycarbonate is 280.degree. F. at 264 psi.
Polycarbonate has a V-50 0.22 cal FSP (fragment simulating projectile) impacting rating of 925 ft./sec. This means that 50% of 22-caliber projectiles fired through a 0.250" polycarbonate sheet penetrate a 20 mils-thick 2024 T6 aluminum sheet (the "witness sheet") placed 6 inches behind the back surface of the poly carbonate sheet.
U.S. Pat. No. 3,866,242, which is incorporated herein by reference, discloses a polyurethane polymer protective shield. The polyurethane is produced by:
(a) reacting either a polyether glycol or a polyester glycol having a molecular weight of about 700 to 1,000 with methylenebis(cyclohexyl isocyanate) in an equivalent ratio of about three NCO to each hydroxyl to form a prepolymer, and PA1 (b) reacting the prepolymer with an aromatic amine curing agent having a methylene bridge between two aromatic rings, such as 4,4'-methylenebis(2-chloroaniline), in an equivalent ratio of 0.90 to 1.04 NH.sub.2 /1.0 NCO. PA1 LONZACURE.RTM. M-DIPA: R.sub.1 .dbd.C.sub.3 H.sub.7 ; R.sub.2 .dbd.C.sub.3 H.sub.7 ; R.sub.3 .dbd.H PA1 LONZACURE.RTM. M-DMA: R.sub.1 .dbd.CH.sub.3 ; R.sub.2 .dbd.CH.sub.3 ; R.sub.3 .dbd.H PA1 LONZACURE.RTM. M-MEA: R.sub.1 .dbd.CH.sub.3 ; R.sub.2 .dbd.C.sub.2 H.sub.5 ; R.sub.3 .dbd.H PA1 LONZACURE.RTM. M-DEA: R.sub.1 .dbd.C.sub.2 H.sub.5 ; R.sub.2 .dbd.C.sub.2 H.sub.5 ; R.sub.3 .dbd.H PA1 LONZACURE.RTM. M-MIPA: R.sub.1 .dbd.CH.sub.3 ; R.sub.2 .dbd.C.sub.3 H.sub.7 ; R.sub.3 .dbd.H PA1 LONZACURE.RTM. M-CDEA: R.sub.1 .dbd.C.sub.2 H.sub.5 ; R.sub.2 .dbd.C.sub.2 H.sub.5 ; R.sub.3 .dbd.Cl
U.S. Pat. No. 4,808,690, which is incorporated by reference herein, discloses a transparent polyurethane polymer made from a polyol cured prepolymer. The prepolymer is made from a polyisocyanate and at least one multifunctional hydroxy-containing intermediate.